Discharge electrode

ABSTRACT

Heretofore, silicon nitride film formed by low pressure plasma CVD has been used for an antireflection film of a solar battery. But it is difficult to reduce the production cost of a solar battery, because, in a low pressure process, facility cost and process cost are expensive. As disclosed, a nitride film is formed by atmospheric pressure plasma CVD using dielectric barrier discharge generated by a plasma head where a plurality of plasma head unit parts is installed in parallel to generate plasma by applying electric field or magnetic field via a dielectric member. Stable glow discharge is formed even under atmospheric pressure by dielectric barrier discharge. And nitride film deposition under atmospheric pressure and low cost production of a solar battery is materialized by using dielectric barrier discharge and by reacting different plasmas generated from plasma supply openings laying side-by-side.

TECHNICAL FIELD

The present invention relates to an atmospheric CVD apparatus usingdielectric-barrier discharge plasma and a method for forming CVD filmusing the plasma, and more particularly, a method for forming a nitridefilm using an atmospheric CVD apparatus.

CITATION LIST Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 1983-220477-   Patent Document 2: Japanese Unexamined Patent Application    Publication No. 2002-110671-   Patent Document 3: Japanese Unexamined Patent Application    Publication No. 2002-176119-   Patent Document 4: Japanese Unexamined Patent Application    Publication No. 2008-98128-   Patent Document 5: Japanese Unexamined Patent Application    Publication No. 2004-39993-   Patent Document 6: Japanese Unexamined Patent Application    Publication No. 1988-50025

BACKGROUND ART

In recent years, solar power generation has been widely used as cleanenergy serving as a substitute for oil-based energy having many problemssuch as resource depletion and the emission of greenhouse gases. Patentdocument 1 discloses a method to enhance energy conversion efficiency byusing silicon nitride film for an antireflection film of a silicon solarbattery. Previously, in plasma CVD processing to form a silicon nitridefilm, a deposition process has been done under reduced pressure of 10⁻²to several Torr in order to create stable plasma. Therefore, productioncost reduction has been difficult because an expensive equipment andpressure reduction process in a deposition chamber are necessary. Formore widespread use of solar power generation, it has been desired todevelop a CVD apparatus and a production method to produce solar batteryat lower cost.

Patent document 2 discloses a technology to produce a thin film byatmospheric CVD. FIG. 12 shows a cross-sectional diagram of an existingatmospheric CVD apparatus disclosed in patent document 2. In general, itis known that stable plasma state cannot be kept under atmosphericpressure when most gases are used except specific gases such as helium,and the plasma state instantly moves into an arc discharge state. In aCVD apparatus as illustrated in FIG. 12, a pair of electrodes 114 and115 are placed facing each other in a chamber 111. And material gasesare introduced from gas inlets 111 and plasma 118 is generated via soliddielectric members 116, 117 by applying electric field on electrodes114, 115. Then a thin film 120 is formed on a substrate 121 by theplasma 118 being sprayed from a supply opening 119. Stable glowdischarge plasma can be generated regardless of the difference of gas byapplying electric field of the electrode via solid dielectric body. Amethod to form a nitride film is described in embodiment 3 of PatentDocument 2. In this method, plasma is generated by introducing a mixturegas of silane gas and ammonia gas diluted by argon gas into a container111. However, silicon plasma and nitrogen plasma do not react on thesubstrate but mainly react in the container according to this method.Therefore almost no nitride film can be formed on the substrate.

In Patent Document 3, a technology to produce thin film by atmosphericCVD is also disclosed. The deposition method disclosed in PatentDocument 3 is film deposition in discharged space, while the depositionmethod disclosed in Patent Document 2 is film deposition by plasmaspray. Accordingly, a nitride film deposition on the substrate becomespossible, but a difference of film deposition rate between regionsaround gas inlet and gas outlet becomes notable. This has lowered thefilm deposition uniformity when several different gases are introducedin those cases such as a nitride film deposition. And a substrate issubject to damage from plasma because the substrate is placed in adischarged space.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

The object of this invention is to provide an atmospheric CVD apparatuswhich enables film formation with high deposition rate and highuniformity. The object of this invention is mainly to provide a CVDapparatus which enables nitride film formation under atmosphericpressure.

Means for Solving Problem

Present invention (1) is a plasma CVD apparatus wherein a desired numberof flow passage plates are stacked and discharge electrodes are placedat the gas outlet side of the flow passage plates, each dischargeelectrode composed of a ceramic member having a hollow portion where anelectrode wire is placed without contact with the ceramic member.

Present invention (2) is the plasma CVD apparatus according to claim 1,characterized in that a gas flow passage is formed along the side of theflow passage plate.

Present invention (3) is the plasma CVD apparatus according to anyone ofclaim 1 or 2, characterized in that the hollow portion is in a vacuumstate.

Present invention (4) is the plasma CVD apparatus according to any oneof claim 1 or 2, characterized in that gas is enclosed in the hollowportion and the gas is noble gas.

Present invention (5) is the plasma CVD apparatus according to claim 4,characterized in that the pressure in the hollow portion is reduced toless than or equal to 250 Torr.

Present invention (6) is the plasma CVD apparatus according to any oneof claim 4 or 5, characterized in that the noble gas is Ar or Ne.

Present invention (7) is the plasma CVD apparatus according to any oneof claims 1 to 6, characterized in that one terminal of the electrodewire was connected to a metal foil, the end of the metal foil functionsas an external extraction terminal, and the metal foil is sealed incontact with narrowed part of the ceramic member.

Present invention (8) is the plasma CVD apparatus according to any oneof claims 1 to 7, characterized in that the electrode wire is made of Nior Ni alloy.

Present invention (9) is the plasma CVD apparatus according to any oneof claims 1 to 7, characterized in that the electrode wire is made of Wincluding Th or ThO.

Present invention (10) is the plasma CVD apparatus according to claim 9,characterized in that the content of Th is less than or equal to 4weight %.

Present invention (11) is the plasma CVD apparatus according to any oneof claims 1 to 10, characterized in that the electrode wire is formedwith coil-like shape.

Present invention (12) is the plasma CVD apparatus according to any oneof claims 1 to 11, characterized in that a layer made of emittermaterial is formed on the surface of the electrode wire, and the emittermaterial is material with smaller work function than the material of theelectrode.

Present invention (13) is the plasma CVD apparatus according to claim12, characterized in that the emitter material is material withperovskite-type crystal structure.

Present invention (14) is the plasma CVD apparatus according to any oneof claim 12 or 13, characterized in that the emitter material is morethan or equal to one chemical compound selected from the chemicalcompound group comprising TiSrO, MgO, TiO.

Present invention (15) is the plasma CVD apparatus according to any oneof claims 12 to 14, characterized in that the emitter layer is formed bya process wherein material of emitter layer is torn into pieces in amortar, and resultant powder is solved in water, and the solution mixedwith glue is coated on the surface of the electrode wire, and emitterlayer is formed by sintering of coated wire.

Present invention (16) is the plasma CVD apparatus according to any oneof claims 12 to 14, characterized in that the emitter layer is formed byMOCVD.

Present invention (17) is the plasma CVD apparatus according to any oneof claims 7 to 16, characterized in that the metal foil is made of Mo orMo alloy.

Present invention (18) is a plasma CVD apparatus wherein a desirednumber of flow passage plates are stacked and discharge electrodes areplaced at the gas outlet side of the flow passage plates, each dischargeelectrode composed of a ceramic member where an electrode wire or ametal foil are enclosed inside the ceramic member.

Present invention (19) is the plasma CVD apparatus according to claim18, characterized in that a gas flow passage is formed along the side ofthe flow passage plate.

Present invention (20) is the plasma CVD apparatus according to any oneof claim 18 or 19, characterized in that the metal foil is made of Mo orMo alloy.

Present invention (21) is the plasma CVD apparatus according to any oneof claims 1 to 20, characterized in that the ceramic member is made ofquartz.

Present invention (22) is the plasma CVD apparatus according to any oneof claims 1 to 20, characterized in that the ceramic member is made oftranslucent alumina.

Present invention (23) is the plasma CVD apparatus according to any oneof claims 1 to 22, characterized in that the flow passage plate is madeof heat resisting metal.

Present invention (24) is the plasma CVD apparatus according to any oneof claims 1 to 22, characterized in that the flow passage plate was madeof ceramic.

Present invention (25) is the plasma CVD apparatus according to any oneof claims 1 to 24, characterized in that the flow passage plate isequipped with a mortise at the gas outlet side, the discharge electrodeis equipped with a tenon at one side, and the discharge electrode isconnected with the flow passage plate by setting in using tenon andmortise.

Present invention (26) is the plasma CVD apparatus according to any oneof claims 1 to 24, characterized in that the discharge electrode isconnected with the flow passage plate using a retainer.

Present invention (27) is the plasma CVD apparatus according to any oneof claims 1 to 24, characterized in that the flow passage plate and thedischarge electrode are fabricated by integral molding.

Present invention (28) is the plasma CVD apparatus according to claim27, characterized in that the gas flow passage the flow passage plate isprocessed after the integral molding of the flow passage plate and thedischarge electrode.

Present invention (29) is the plasma CVD apparatus according to claim27, characterized in that the gas flow passage the flow passage plate isprocessed at the same time as the integral molding of the flow passageplate and the discharge electrode.

Present invention (30) is the plasma CVD apparatus according to any oneof claims 1 to 29, characterized in that a substrate is placed facing tothe discharge electrode.

Present invention (31) is the plasma CVD apparatus according to claim30, characterized in that the substrate can be conveyed.

Present invention (32) is the plasma CVD apparatus according to claim31, characterized in that the substrate is a substrate with band-likeshape which is conveyed by roll-to-roll process.

Present invention (33) is the plasma CVD apparatus according to any oneof claims 1 to 32, characterized in that the apparatus is an apparatusfor the deposition of silicon nitride film.

Present invention (34) is the plasma CVD apparatus according to any oneof claims 1 to 32, characterized in that the apparatus is an apparatusfor the deposition of silicon film.

Present invention (35) is the plasma CVD apparatus according to anyoneof claims 1 to 34, characterized in that at least nitrogen source gasand silicon source gas are supplied through the flow passage plates, andnitrogen source gas and silicon source gas are respectively suppliedthrough different flow passage plates.

Present invention (36) is the plasma CVD apparatus according to any oneof claims 1 to 34, characterized in that at least mixed gas of nitrogensource gas and silicon source gas is supplied through the flow passageplates.

Present invention (37) is the plasma CVD apparatus according to any oneof claims 33 to 36, characterized in that the silicon nitride film orsilicon film is deposited consecutively.

Present invention (38) is the plasma CVD apparatus according to any oneof claims 1 to 37, characterized in that the gas outlet is placeddownward.

Present invention (39) is the plasma CVD apparatus according to any oneof claims 1 to 37, characterized in that the gas outlet is placed towardlateral direction.

Present invention (40) is the plasma CVD apparatus according to any oneof claims 31 to 39, characterized in that deposition process is carriedout while positive bias voltages and negative bias voltages arealternatively applied to a plurality of neighboring discharge electrodesand negative voltage is applied to the substrate.

Present invention (41) is the plasma CVD apparatus according to any oneof claims 1 to 39, characterized in that deposition process is carriedout while positive bias voltages and negative bias voltages arealternatively applied to a plurality of neighboring discharge electrodesand the substrate is set to be floating potential.

Present invention (42) is the plasma CVD apparatus according to any oneof claims 31 to 39, characterized in that deposition process is carriedout while positive bias voltage is applied to a plurality of dischargeelectrodes and negative voltage is applied to the substrate.

Present invention (43) is the plasma CVD apparatus according to any oneof claims 40 to 41, characterized in that deposition process is carriedout while a dielectric substrate is placed under the substrate, andpositive bias voltage is applied to the dielectric substrate.

Present invention (44) is the plasma CVD apparatus according to any oneof claims 1 to 43, characterized in that deposition process is carriedout while the discharge electrode is cooled down by noble gas or inertgas.

Present invention (45) is the plasma CVD apparatus according to any oneof claims 1 to 44, characterized in that plasma was generated under RFor pulse electric field at lower or higher frequency than 13.56 MHz.

Present invention (46) is the plasma CVD apparatus according to any oneof claims 1 to 45, characterized in that a movable quartz member is fitin a space in the gas passage.

Present invention (47) is a discharge electrode composed of a ceramicmember having a hollow portion where an electrode wire is placed withoutcontact with the ceramic member

Present invention (48) is the discharge electrode according to claim 47,characterized in that the hollow portion is in vacuum state.

Present invention (49) is the discharge electrode according to claim 47,characterized in that gas is enclosed in the hollow portion and the gasis noble gas.

Present invention (50) is the discharge electrode according to claim 49,characterized in that the pressure in the hollow portion is reduced toless than or equal to 250 Torr.

Present invention (51) is the discharge electrode according to any oneof claim 49 or 50, characterized in that the noble gas is Ar or Ne

Present invention (52) is the discharge electrode according to any oneof claim 47 or 51, characterized in that one terminal of the electrodewire was connected to a metal foil, the end of the metal foil functionsas an external extraction terminal, and the metal foil is sealed incontact with narrowed part of the ceramic member.

Present invention (53) is the discharge electrode according to any oneof claim 47 or 52, characterized in that the electrode wire is made ofNi or Ni alloy.

Present invention (54) is the discharge electrode according to any oneof claim 47 or 53, characterized in that the electrode wire is made of Wincluding Th or ThO.

Present invention (55) is the discharge electrode according to claim 54,characterized in that the content of Th is less than or equal to 4weight %.

Present invention (56) is the discharge electrode according to any oneof claim 47 or 55, characterized in that the electrode wire is formedwith coil-like shape.

Present invention (57) is the discharge electrode according to any oneof claim 47 or 56, characterized in that a layer made of emittermaterial is formed on the surface of the electrode wire, and the emittermaterial is material with smaller work function than the material of theelectrode.

Present invention (58) is the discharge electrode according to claim 57,characterized in that the emitter material is material withperovskite-type crystal structure.

Present invention (59) is the discharge electrode according to any oneof claim 57 or 58, characterized in that the emitter material is morethan or equal to one chemical compound selected from the chemicalcompound group comprising TiSrO, MgO, TiO.

Present invention (60) is the discharge electrode according to any oneof claim 57 or 59, characterized in that the emitter layer is formed bya process wherein material of emitter layer is torn into pieces in amortar, and resultant powder is solved in water, and the solution mixedwith glue is coated on the surface of the electrode wire, and emitterlayer is formed by sintering of coated wire.

Present invention (61) is the discharge electrode according to any oneof claim 57 or 59, characterized in that the emitter layer is formed byMOCVD.

Present invention (62) is the discharge electrode according to any oneof claim 52 or 61, characterized in that the metal foil is made of Mo orMo alloy.

Present invention (63) is a method for forming CVD film using the plasmaCVD apparatus according to any one of claim 1 or 46.

Effect of the Invention

According to present invention (1), (6), (7), (47), (51), (52), (63),stable glow discharge plasma can be generated even under atmosphericpressure, then high rate deposition of nitride film with excellentuniformity in film thickness. Low cost mass production of solar batterycan be achieved.

According to present invention (2)-(5), (48)-(50), stable plasmageneration due to glow discharge can be more easily achieved.

According to present invention (8)-(10), (53)-(55), the work function ofan electrode wire can be reduced so as to enhance thermal electronemission.

According to present invention (11), (56), discharge area can beenlarged due to the increase in the surface area of an electrode wire.

According to present invention (12)-(15), (57)-(60), electrons areemitted not only from an electrode wire but also from emitter materialso that discharge starts by lower power supply and discharge state afterthe start becomes more stable.

According to present invention (16), (61), the space in a coil can besufficiently filled by emitter material. And emitter material can beformed more densely, and its compositional ratio can be improved.

According to present invention (17), (62), adhesion of the metal foilwith ceramic member can be improved.

According to present invention (18), stable glow discharge plasma can begenerated even under atmospheric pressure, then high rate deposition ofnitride film with excellent uniformity in film thickness. Low cost massproduction of solar battery can be achieved. And the electrode does nothave a hollow portion so that it is easier to fabricate a CVD apparatus.

According to present invention (19)-(22), stable plasma generation dueto glow discharge can be more easily achieved.

According to present invention (23), thermal deformation of the flowpassage plate can be prevented due to heat producing electrode.

According to present invention (24), ceramic is excellent heat resistingmaterial and the difference of its coefficient of thermal expansion fromthat of an electrode is small.

According to present invention (25), existing flow passage plates can beutilized.

According to present invention (26), tenon and mortise processing is notnecessary and quick-release is possible.

According to present invention (27)-(29), it becomes easier to fabricatethe apparatus.

According to present invention (30), stable glow discharge plasma can begenerated more easily.

According to present invention (31), (32), a large area film withexcellent uniformity in thickness can be deposited.

According to present invention (33), (34), low cost production of usefulelectronic devices such as a solar battery.

According to present invention (35), silicon nitride film and siliconfilm with high purity can be deposited using a single apparatus.

According to present invention (36), the configuration of an apparatuscan be simplified.

According to present invention (37), a large area film with excellentuniformity in thickness can be deposited.

According to present invention (38), the uniformity of deposited filmcan be improved.

According to present invention (39), installation area of an apparatuscan be minimized.

According to present invention (40), stable glow discharge plasma can begenerated more easily. Deposition rate can be enhanced because plasmacan be generated in larger region. And the collision damage to thesubstrate by positive ions such as Ar ions can be weakened. The damageof deposited thin film on the substrate can be reduced so that denserthin film can be formed.

According to present invention (41), (42), stable glow discharge plasmacan be generated more easily.

According to present invention (43), the collision damage to thesubstrate by positive ions such as Ar ions can be weakened. The damageof deposited thin film on the substrate can be reduced so that denserthin film can be formed.

According to present invention (44), the over-heat of the dischargeelectrode can be prevented.

According to present invention (45), power supply at frequency otherthan 13.56 MHz which is commonly used in a plasma apparatus can beutilized for a deposition process. By controlling the frequency, it ispossible to minimize the damage to a thin film on the substrate.

According to present invention (46), it is possible to control thecross-sectional area of a gas passage so that plasma state or filmdeposition state can be optimized.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram of the structure of an electrode in a CVD apparatusaccording to the present invention.

FIG. 2(a) and FIG. 2(b) are diagrams to show process steps to fabricatethe electrode in a CVD apparatus according to the present invention.

FIG. 3(a) is a front view diagram of a plasma head according to thefirst specific example of the present invention. FIG. 3(b) and FIG. 3(c)are side view diagrams of a plasma head according to the first specificexample of the present invention.

FIG. 4(a) and FIG. 4(b) are respectively a front view diagram and a sideview diagram of a plasma head according to the second specific exampleof the present invention.

FIG. 5(a) is a front view diagram of a plasma head unit member accordingto the first specific example of the present invention.

FIG. 5(b) and FIG. 5(c) are side view diagrams of a plasma head unitmember according to the first specific example of the present invention.

FIG. 6(a) is a front view diagram of a plasma head unit member accordingto the second specific example of the present invention.

FIG. 6(b) and FIG. 6(c) are side view diagrams of a plasma headaccording to the second specific example of the present invention.

FIG. 7(a) is a front view diagram of a plasma head unit member accordingto the third specific example of the present invention.

FIG. 7(b) and FIG. 7(c) are side view diagrams of a plasma headaccording to the third specific example of the present invention.

FIG. 8 is a cross-sectional diagram of a CVD apparatus according to theembodiment of the present invention.

FIG. 9(a), FIG. 9(b), and FIG. 9(c) are cross-sectional diagrams of aplasma head in a CVD apparatus according to of the embodiment of thepresent invention.

FIG. 10 is a cross-sectional diagram of a plasma head in a CVD apparatusaccording to the embodiment of the present invention.

FIG. 11(a), FIG. 11(b), and FIG. 11(c) are cross-sectional diagrams of aflow passage plate in a CVD apparatus according to the embodiment of thepresent invention.

FIG. 12 is a cross-sectional diagram of a flow passage plate in aconventional CVD apparatus.

DESCRIPTION OF THE SYMBOLS

-   1, 2, 3: plasma head unit member-   4, 11, 15: gas inlet-   5, 12, 16: dielectric member-   6, 13, 17: plasma generation passage-   7, 14, 18: plasma supply opening-   8, 9: electrode-   10: shock absorbing member-   21, 22, 23: plasma head unit member-   24, 35: gas distribution passage-   25, 33: dielectric member-   26, 36: plasma generation passage-   27, 37: plasma supply opening-   28, 29: electrode-   30: shock absorbing member-   31: gas distribution passage region-   32: plasma generation passage region-   34: gas supply pipe-   41, 47, 51: gas introduction opening-   42, 48, 52: dielectric member-   43, 49, 53: plasma generation passage-   44, 50, 54: plasma supply opening-   45, 46: electrode-   61, 66, 71: gas introduction opening-   62, 67, 72: dielectric member-   63, 68, 73: plasma generation passage-   65, 70, 75: plasma supply opening-   64, 69, 74: induction coil-   81, 88, 95: gas introduction opening-   82, 89, 96: dielectric member-   83, 90, 97: plasma generation passage-   85, 91, 98: plasma supply opening-   84, 92, 99: induction coil-   86, 87, 93, 94: coil terminal-   101, 102: source gas supply unit-   103: power source-   104: plasma head-   105, 106: plasma-   107: plasma reaction region-   108: thin film-   109: substrate-   110: substrate conveyance unit-   111: gas introduction opening-   112: power source-   113: container-   114, 115: electrode-   116, 117: solid dielectric body-   118: plasma-   119: plasma supply opening-   120: thin film-   121: substrate-   201, 202: flow passage plate-   203, 204: quartz member-   205, 206: electrode wire-   207, 208: gas flow direction-   209: substrate-   210: support member-   211, 215: quartz member-   212, 216: electrode wire-   213, 217: electrode lead wire-   214: opening-   218: enclosing member-   301, 306, 311, 321: flow passage plate-   302, 307, 312, 322: discharge electrode-   303, 308, 313, 323: plasma-   304, 309, 314, 324: substrate-   305, 310, 315, 325: dielectric substrate-   326: electrode for applying bias voltage-   327: power source for applying bias voltage-   328: positive argon ion-   331, 335, 339: flow passage plate-   332, 336, 340: flow passage-   333, 334, 337, 338, 341, 342: dielectric member

BEST MODE EMBODIMENTS FOR CARRYING OUT THE INVENTION

Best mode embodiments for carrying out the present invention aredescribed in detail as follows.

(Glow Discharge by Dielectric-Barrier Discharge)

Inventors of the present invention have earnestly studied plasmadeposition for realization of silicon nitride CVD under atmosphericpressure. First they have employed plasma-blowing deposition forpreventing plasma damage on a substrate, and have employed plasmaformation by dielectric-barrier discharge for stable glow discharge. Inorder to prevent plasma reaction in a plasma generation chamber whichwas a problem of conventional method, a plasma head, which is a plasmageneration member, is composed of a plurality of unit parts respectivelyhaving an independent plasma blow opening. For example, silicon plasmaand nitrogen plasma are generated separately in each unit part insilicon nitride CVD process. Furthermore inventors have discovered thatthe parallel configuration wherein a unit part for silicon plasmageneration is placed next to a unit part for nitrogen plasma generationis effective for improvement in uniformity of deposited film. Plasmasupplied from a blow opening does not react in a plasma head, but itreacts in a space between a blow opening and a substrate to depositsilicon nitride film. Therefore highly effective silicon nitridedeposition on a substrate becomes possible. And also, material gases aresupplied independently to each unit parts of the plasma head, andelectrodes are placed so that electrical energy can be controlledindependently which is applied for plasma generation. By thesearrangements, thin film deposition becomes possible using bestconditions for each plasma generation.

And also, in conventional method, there is a problem that it isdifficult to generate continuously stable plasma when plasma isgenerated under atmospheric pressure. Inventors of the present inventionhave taken notice of the structure of an electrode and the structure ofa part where a substrate is placed. And they have discovered that stableplasma generation, the enhancement of nitride film deposition rate, andthe improvement of reproducibility in film thickness and film qualitybecome possible by the arrangement wherein an electrode is enclosed in aquartz member, and the electrode is separated from the quartz member byempty space, and a substrate is placed on a quartz supporting member,and plasma is supplied from a plasma head to the substrate.

In addition, “atmospheric pressure” in this specification specificallymeans pressure between 8×10⁴ and 12×10⁴ Pa, while it depends on theatmospheric pressure and the altitude of the place where the CVDapparatus is placed. When the pressure of CVD process is within thisrange, it is possible to reduce facility cost because expensiveequipment for compression and decompression is not needed.

(Specific Example of an Electrode Structure)

FIG. 1 is a diagram of the structure in a CVD apparatus according to thepresent invention. Quartz members 203, 204 are placed in the gas blowoutopenings of flow passage plates 201, 202 where process gas flows, andelectrode wires 205, 206 are placed in the hollow portion of the quartzmembers 203, 204. Electrical energy due to discharge between electrodewires 205, 206 and a substrate 209 is applied to gas molecules ofprocess gas which blows out from the gas blowout openings of flowpassage plates 201, 202. Then the molecules are transformed into plasmawhich is supplied to the substrate 209, and silicon nitride film isdeposited on the substrate 209 by the reaction of ions in the plasma.Electrode wires 205, 206 are preferably placed in the hollow portion ofthe quartz members 203, 204 without direct contact between them. Theambient of the hollow portion is preferably vacuum state or low-pressurestate. When the ambient is low-pressure state, gas enclosed in thehollow portion is preferably noble gas such as Ar, or Ne. Preferablerange of the low pressure is less than or equal to 250 Torr. Plasma isspontaneously generated by less power supply, and stable plasmageneration becomes possible by uniform discharge when the hollow portionis evacuated or depressurized at the pressure less than or equal to 250Torr with the ambient of noble gas. Flow passage plates 201, 202 arefabricated, for example, by processing aluminum plate. The substrate 209is preferably placed on a quartz supporting member 210. Then thestability of plasma is enhanced. The shape of the quartz members 203,204 is not limited to the specific shape if they have long hollow partso that linear electrode can be placed inside. The cross-sectional shapeof the hollow portion is not limited to the specific shape, but it ispreferably a circle. And the quartz members are preferably equipped withconvex parts so that they can be set in the flow passage plates. Theflow passage plates are equipped with concave parts corresponding to theconvex parts. Alternatively, the quartz members can be equipped withconcave parts and the flow passage plates can be equipped with convexparts corresponding to the concave parts.

And also, electrodes can be placed under the supporting member 210 forcontrolling bias voltage applied to the plasma. In this case, electrodesplaced above the substrate 209, such as electrodes 205, 206, are calledas upper electrodes, and electrodes placed under the substrate 209(under the supporting member 210) are called as lower electrodes.

As shown in FIG. 1, main body of a flow passage plate and an electrodecan be fabricated as separate parts, and can be set in using tenon andmortise. Alternatively, an electrode can be placed under the flowpassage plate using a retainer. A process to make mortise trench is notnecessary, and it becomes easier to remove and replace these parts. Andalso, main body of a flow passage plate and an electrode can befabricated by integral molding. The process to fabricate an apparatusbecomes easier. A flow passage can be processed after the integralmolding of a flow passage plate and an electrode. Or it can be processedat the same time as the integral molding.

It is found that plasma is not generated when nitrogen or ammonia gaswhich is process gas for nitride film deposition is introduced from thebeginning of the process, but plasma can be generated when Ar gas isintroduced. Therefore, it is found that plasma which is necessary fornitride film deposition can be stably generated by process stepscharacterized in that plasma is generated by introducing Ar gas first,and then the number of electrons is increased, and then the flow rate ofnitrogen or ammonia gas is gradually increased.

In the embodiment as shown in FIG. 1, electrode wires are not placed indirect contact with quartz members, and they are placed as floatingstatus in a hollow portion. Alternatively, electrode wires can be placedin direct contact with quartz members without making a hollow portion,which makes fabrication of plasma head easier. The material of electrodewires or metal foil is preferably Mo or Mo alloy. Mo or Mo alloy ishighly adhesive with ceramics.

The material of an insulating member of the electrode which correspondsto the above-mentioned members 203, 204 is preferably ceramics in bothcases where a hollow portion is prepared or not around the electrode.Furthermore the material is preferably quartz or translucent alumina.And the material of the flow passage plate is preferably heat-resistantmetal or ceramics.

The structure of an electrode used in the conventional CVD apparatus isthe structure where carbon members are exposed, so there is a leakageproblem of impurities included in carbon material. Meanwhile, there isno leakage problem of impurities in the structure of the electrodeaccording to the present invention wherein an electrode wire is coveredby a quartz tube.

The material of an electrode wire is preferably W. It is more preferablyW which contains Th or ThO. The content of Th is preferably less than orequal to 4% by weight. This arrangement reduces the work function of theelectrode wire, and facilitates the emission of thermal electrons sothat plasma can be easily generated.

It is preferable that an electrode wire is entirely heated byappropriate external current supply to the wire. When the temperature ofthe wire is low, nitride or silicon film can be deposited on the surfaceof the electrode. Then it is not preferable because the flow passage maybe reduced in thickness or clogged up. To the contrary, it is possibleto prevent the growth of deposited material on the surface of theelectrode by heating it. And also, it is possible to control the workfunction of metal such as Th or PTO which is added to electrode materialsuch as W by controlling the temperature of the electrode. By thesearrangements, electron density emitted from metal can be controlled sothat CVD process can be controlled more precisely.

And radioactive material is preferably coated on the surface ofelectrode material. For example, strontium is preferably coated. Plasmacan be easily excited by coating radioactive material.

And also, material with smaller work function than the material of theelectrode is preferably used as emitter material, and a layer of theemitter material is preferably formed on the surface of the electrodewire. Material with perovskite-type crystal structure is preferably usedas the emitter material. And more than or equal to one chemical compoundselected from the chemical compound group comprising TiSrO, MgO, TiO ispreferably used as the material. Any of these arrangements reduces thework function of the electrode wire, and facilitates the emission ofthermal electrons so that plasma can be easily generated.

The emitter layer is formed by a process wherein material of emitterlayer is torn into pieces in a mortar, and resultant powder is solved inwater, and the solution mixed with glue is coated on the surface of theelectrode wire, and emitter layer is formed by sintering of coated wire.Or it can be formed by MOCVD. When the electrode wire is formed withcoil-like shape, space formed in the electrode can be sufficientlyfilled by emitter material. And the emitter layer can be formed moredensely, and its composition ratio can be improved.

And also, a quartz electrode placed in a quartz member is preferablyused not only for an electrode for high frequency radiation but alsoused for a heater. The temperature control of a body on which depositionfilm is formed can be controlled, for example, by heating, by using thequartz electrode as a heater.

(Method for Fabricating an Electrode)

FIG. 2(a) and FIG. 2(b) are diagrams to show process steps to fabricatethe electrode in a CVD apparatus according to the present invention.First, as shown in FIG. 2(a), a quartz member 214 with a hollow portionis prepared having one terminal with an opening 214 and the other closedterminal. As an electrode wire 212, for example, a wire made of Ni or Nialloy is used. In FIG. 2(a) and FIG. 2(b), a linear electrode wire isshown, but an electrode wire with coil-like shape is preferably used.The surface area of the electrode can be enlarged, and the dischargearea can be also enlarged by using an electrode with coil-like shape. Alead wire 213 is attached on the terminal of an electrode 212. As a leadwire, for example, metal foil with a thickness of about 20 μm made of Moor Mo alloy is used. Next, the inside of the quartz member 211 isdepressurized until the pressure reaches to vacuum or less than or equalto 250 Torr. Then the opening 214 is enclosed as shown in FIG. 2 (b).According to these process steps, an electrode member is completed wherean electrode 216 is supported by a lead wire 217 in a floating statewithout contact with a quartz member 215.

Noble gas such as Ar or Ne is preferably used for filler gas when ahollow portion is depressurized. It is more preferable that clean gassuch as Ar with impurity concentration less than or equal to 10 ppb isintroduced as purge gas into the hollow portion before the filler gas isintroduced.

(The First Specific Example of a Unit Part of a Plasma Head)

FIG. 5(a) and FIG. 5(c) are respectively a front view diagram and a sideview diagram of a plasma head according to the first specific example ofthe present invention. The first specific example of a unit part is aunit part of a plasma head to generate capacitance coupling plasma. Theunit part comprises a dielectric member 42 and a pair of electrodes 45,46 which hold a dielectric member 42. The dielectric member 42 isequipped with a hole which passes through from top down, and the holefunctions as a plasma generation passage. The dielectric member 42 canbe formed as an integral member, or it can be formed by pasting orfitting a plurality of members together. When the dielectric member iscomposed of a plurality of members, it is preferably processed so thatno leakage occurs at a joint part. One end of the hole is used as a gasintroduction opening 41. Then electrical field is applied to theelectrode 45, 46 which provides electrical energy to introduced gasmolecules to generate plasma made of radicals, ions, and electrons.Constant, high-frequency, or pulsed electrical field can be preferablyapplied. Especially, pulsed electrical field can be preferably applied.Electrical field is applied via dielectric member, so even when constantelectrical field is applied, accumulation and extinction of charge arerepeated one after the other on the surface of dielectric member.Accordingly, plasma discharge state does not reach to be arc dischargebut becomes stable glow discharge. Generated plasma blows out fromplasma supply opening 50 which is the other end of the hole. The rangewhere plasma is supplied depends on the condition of plasma generation,but generally speaking, plasma is supplied in the range of severalmm-several cm from plasma supply opening 50. As shown in the side viewdiagram of FIG. 3(b), the unit part can be equipped with one plasmasupply opening. And as shown in FIG. 5(c), it can be equipped with aplurality of plasma supply openings. When a deposition process isapplied on a small substrate, plasma can be supplied from one plasmasupply opening. When a deposition process is applied on a largesubstrate, plasma is preferably supplied from a plurality of plasmasupply openings for better uniformity of deposition.

And also it is not necessary that a hole is prepared for a gas passagein dielectric member as shown in FIG. 5(a), FIG. 5(b), and FIG. 5(c). Aspace between dielectric members can be used as a gas passage when thedielectric members are placed parallel to each other with a spacebetween them.

Material of dielectric members is preferably plastic, glass, carbondioxide, metal oxide such as aluminum oxide. Especially, quartz glass ispreferably used. Dielectric material with relative permittivity greaterthan or equal to 2 is preferably used. Dielectric material with relativepermittivity greater than or equal to 10 is more preferably used. Thethickness of dielectric material is preferably in the range from 0.01 mmto 4 mm. If it is too thick, excessively high voltage is necessary forplasma generation. If it is too thin, arc discharge tends to take place.

Material of electrode is preferably metal such as copper, aluminum,stainless-steel or metal alloy. The distance between electrodes, whichdepends on the thickness of dielectric member and applied voltage, ispreferably in the range from 0.1 mm to 50 mm.

(The Structure of a Plasma Head) (The First Specific Example of a PlasmaHead)

FIG. 3 (a) is a front view diagram of a plasma head according to thefirst specific example of the present invention. FIG. 3(b) and FIG. 3(c)are side view diagrams of a plasma head according to the first specificexample of the present invention. Plasma head is formed by sequentiallyinstalling one of a plurality of unit parts adjacent to the otherincluding plasma head unit members 1, 2, 3. In FIG. 3 (a), plasma headunit parts are placed in parallel by inserting shock absorbing member 10between the plasma head unit members. The shock absorbing member is notalways an indispensable part for the plasma head structure. But it isuseful for preventing the damage of dielectric member 5 by inserting theshock absorbing member when the dielectric member 5 is made of materialsubject to breakage such as glass and a plurality of plasma head unitparts is fixed by clenching. According to the structure of unit partsused, a plasma head can be equipped with one plasma supply opening asshown in the side view diagram in FIG. 3 (b), and it can be equippedwith a plurality of plasma supply openings as shown in FIG. 3 (c).

(The Second Specific Example of a Plasma Head)

FIG. 4 (a) and FIG. 4 (b) are respectively a front view diagram and aside view diagram of a plasma head according to the second specificexample of the present invention. Plasma head is formed by sequentiallyinstalling one of a plurality of unit parts adjacent to the otherincluding plasma head unit members 21, 22, 23. As shown in the side viewdiagram in FIG. 2 (b), plasma head is equipped with a plurality ofplasma supply openings. A dielectric member 35 is processed so that itis equipped with a hollow portion inside. This hollow portion functionsas a gas distribution passage and a plasma generation passage. A hollowportion can be formed in the dielectric member as an integral part. Or ahollow portion can be formed by that a concave part is formed in onedielectric plate and the other plate is bonded to the former plate.Material gas for plasma generation is supplied from gas supply opening34. A gas distribution passage region is formed is formed in the upperpart of the dielectric member 35, the region which distributes gassupplied from the gas supply opening 34 into a plurality of plasmageneration passages 36. According to this structure, material gas can beequally supplied to many plasma generation members using a simplestructure so as to contribute downsizing of CVD apparatus.

(The Structure of a CVD Apparatus)

FIG. 8 is a cross-sectional diagram of a CVD apparatus according to theembodiment of the present invention. A CVD apparatus consists of asource gas supply unit 101 supplying the first gas, a source gas supplyunit 102 supplying the second gas, a plasma head 104 which is formed bysequentially installing a plasma head unit part adjacent to a shockabsorbing member, a power supply which supplies electrical power to theplasma head unit part, and a substrate conveyance unit 110 which conveyssubstrates. A plasma head unit part consists of a dielectric memberequipped with plasma generation passage and an electrode. Material gasis introduced from the upper gas introduction opening, and electricfield is applied by an electrode via a dielectric member to excite thematerial gas for generating plasma comprising radicals, ions, andelectrons. Generated plasma is supplied from a plasma supply opening toa substrate 109 placed on the substrate conveyance unit 110. Adeposition process is carried out while substrates are conveyed by asubstrate conveyance unit which enables consecutive deposition. Theshape of the substrate is preferably band-like shape which is conveyedby roll-to-roll process. Or another process can be adopted in which asubstrate is placed on a static position during deposition process, andafter the deposition is finished, the substrate is conveyed so that thenext substrate is in the deposition position by the substrate conveyanceunit.

In addition, a lower electrode which is not shown in the diagram isplaced under the substrate 109, and it can apply bias voltage from underthe substrate.

Plasma supply openings can be placed downward as shown in FIG. 8, orthey can be placed toward lateral direction. When plasma supply openingsare placed downward, the uniformity of deposition can be improved. Whenthey are placed toward lateral direction, the installation area of theapparatus can be minimized.

Because plasma discharge is dielectric barrier discharge, plasma becomesstable glow discharge, and it becomes non-equilibrium plasma where thetemperature of electrons is high and that of radicals and ions is low.

When silicon nitride is deposited, for example, silane gas and ammoniagas are used as material gas. Silane gas and ammonia gas are suppliedalternately to adjacent plasma head unit parts, and silicon plasma 105and nitrogen plasma 106 are generated in each plasma generation passage.Silicon plasma and nitrogen plasma reach downward until several mm toseveral cm from plasma supply opening, then plasma reaction region 107is formed.

When silicon nitride is deposited, other silicon source gas or nitrogensource gas can be used. As silicon source gas, silane, disilane, ormixed gas made of these gases attenuated by inert gas can be used. Asnitrogen source gas, ammonia, nitrogen, or mixed gas made of these gasesattenuated by inert gas can be used.

Silicon nitride film can be deposited by independently supplying siliconsource gas and nitrogen source gas through flow passage plates layingside-by-side among a plurality of flow passage plates. During thisprocess, it is possible to flow curtain-enclosed gas made of inert gassuch as nitrogen through flow passage plates surrounding the plates forsource gases. The flow rate of silicon source gas and nitrogen sourcegas can be independently controlled, which enables precise control ofprocess conditions.

Alternatively, silicon nitride film can be deposited by supplying amixed gas made of silicon source gas and nitrogen source gas throughidentical flow passage plates. The configuration of an apparatus can besimplified.

As another example of deposited film, silicon film can be deposited bynot supplying nitrogen source gas but supplying silicon source gas.

During the excitation of plasma for deposition process, it is preferableto cool down an electrode by introducing a mixed gas comprising orincluding noble gas (for example, Ar and N₂) nearby the electrode in theflow passage plate. When an electrode is not cooled down, and thetemperature of the electrode itself rises by plasma excitation, a filmwhich is not a dielectric member in use or extraneous material isattached on the surface of the electrode, and the function of theelectrode is disabled. To prevent this problem, it is preferable tocirculate cooling gas in a temperature of about 20 deg C.

And also, a movable dielectric member is preferably fit in a space ingas passage or flow passage plate through which process gas or carriergas flows. Quartz is preferably used as a dielectric member. By thisarrangement, it is possible to control the cross-sectional area of flowpassage so that the controllability of the process can be improved. FIG.11(a), FIG. 11(b), and FIG. 11(c) are cross-sectional diagrams of a flowpassage plate in a CVD apparatus according to the practical example ofthe present invention. The cross-sectional area of a flow passage 332(FIG. 11(a)) surrounded by a flow passage plate 331 and dielectricmembers 333, 334 can be controlled by moving the dielectric members 333,334 as shown in a flow passage 336 (FIG. 11(b)) and a flow passage 340(FIG. 11(c)). The flow rate of process gas can be controlled bycontrolling the cross-sectional area of a flow passage. For example, theflow rate can be increased by narrowing the cross-sectional area of aflow passage.

(Plasma Generation Parameters)

Process conditions to generate plasma are appropriately determinedaccording to the purpose to utilize plasma. When capacitance couplingplasma is generated, plasma is generated by applying constant electricfield, high frequency electric field, pulsed electric field, micro-waveelectric field between a pair of electrodes. When electric field isapplied other than constant electric field, the used frequency can be13.56 MHz which is used in a general plasma apparatus, or it can behigher than or lower than 13.56 MHz. In Patent Document 6, a technologyto prevent plasma damage on the deposited film by using high frequencyplasma of 100 MHz in a plasma apparatus is disclosed. By controlling thefrequency of electric field, characteristics such as deposition rate,the quality of deposited film can be optimized.

Pulsed electric field is preferably used for plasma generation. Itsfield intensity is preferably in the range from 10 to 1000 kV/cm. Itsfrequency is preferably higher than or equal to 0.5 kHz.

(Inductive Coupling Plasma Apparatus) (The Second Specific Example of aUnit Part of a Plasma Head)

Technical idea concerning plasma head according to the present inventionis not limited to be applied for a plasma head for capacitance couplingplasma, but for example, it can be applied for a plasma head forinductive coupling plasma.

FIG. 6(a) is a front view diagram of a plasma head unit member accordingto the second specific example of the present invention. FIG. 6(b) andFIG. 6(c) is a side view diagram of a plasma head according to thesecond specific example. The unit part consists of a dielectric members62 and an inductive coil 64 circumferentially placed adjacent to themember. The dielectric members 62 is equipped with a hole which passesthrough from top down, and the hole functions as a plasma generationpassage. The dielectric member 62 can be formed as an integral member,or it can be formed by pasting or fitting a plurality of memberstogether. When the dielectric member is composed of a plurality ofmembers, it is preferably processed so that no leakage occurs at a jointpart. One end of the hole is used as a gas introduction opening 61. Thenelectrical current is applied to the inductive coil 64, and generatedmagnetic field provides magnetic energy to introduced gas molecules togenerate plasma made of radicals, ions, and electrons. Plasma dischargestate becomes stable glow discharge. Generated plasma blows out fromplasma supply opening 65 which is the other end of the hole. The rangewhere plasma is supplied depends on the condition of plasma generation,but generally speaking, plasma is supplied in the range of severalmm-several cm from plasma supply opening 65. As shown in the side viewdiagram of FIG. 6(b), the unit part can be equipped with one plasmasupply opening. And as shown in FIG. 6(c), it can be equipped with aplurality of plasma supply openings. When a deposition process isapplied on a small substrate, plasma can be supplied from one plasmasupply opening. When a deposition process is applied on a largesubstrate, plasma is preferably supplied from a plurality of plasmasupply openings for better uniformity of deposition.

(The Third Specific Example of a Plasma Head)

FIG. 7(a) is a front view diagram of a plasma head unit member accordingto the third specific example of the present invention. FIG. 7(b) andFIG. 7(c) are side view diagrams of a plasma head according to the thirdspecific example. The unit part consists of a dielectric members 82 andan inductive coil 84 placed adjacent to the member. The dielectricmembers 82 is equipped with a hole which passes through from top down,and the hole functions as a plasma generation passage 83. The dielectricmember can be formed as an integral member, or it can be formed bypasting or fitting a plurality of members together. When the dielectricmember is composed of a plurality of members, it is preferably processedso that no leakage occurs at a joint part. The terminals 86, 87 of theinductive coil 84 are placed well away from each other so that they arenot electrically shorted. One end of the hole is used as a gasintroduction opening 81. Then electrical current is applied to theinductive coil 84, and generated magnetic field provides magnetic energyto introduced gas molecules to generate plasma made of radicals, ions,and electrons. Plasma discharge state becomes stable glow discharge.Generated plasma blows out from plasma supply opening 85 which is theother end of the hole. The range where plasma is supplied depends on thecondition of plasma generation, but generally speaking, plasma issupplied in the range of several mm-several cm from plasma supplyopening 85. As shown in the side view diagram of FIG. 7(b), the unitpart can be equipped with one plasma supply opening. And as shown inFIG. 7(c), it can be equipped with a plurality of plasma supplyopenings. When a deposition process is applied on a small substrate,plasma can be supplied from one plasma supply opening. When a depositionprocess is applied on a large substrate, plasma is preferably suppliedfrom a plurality of plasma supply openings for better uniformity ofdeposition.

(Method for Producing a Plasma Head) (Bonding Method)

To fabricate dielectric members making up a plasma head according to thepresent invention, it is necessary to process a hollow portion with acomplicated shape such as a plasma generation passage and a gasdistribution passage. Such a dielectric member with a hollow portion canbe fabricated by bonding dielectric members with a hollow portion or bybonding a dielectric member with a hollow portion and a flat dielectricmember after forming a hollow portion on the surface of a plurality ofdielectric members.

A plasma head unit part is formed by stacking an electrode or aninductive coil on the dielectric member with a hollow portion formed bythis way. Furthermore, a plasma head is formed by stacking a pluralityof plasma head unit parts via a shock absorbing member made of materialsuch as Teflon™.

(Injection Molding Method)

A plasma head unit part can be fabricated by an injection moldingmethod. A hydraulic core and an electrode or an inductive coil areplaced in a mold, and material of a dielectric member is injected in themold, then a fabricated part is unmolded and the hydraulic core isremoved with the electrode or the inductive coil left behind.Furthermore, a plasma head is formed by stacking a plurality of plasmahead unit parts via a shock absorbing member made of material such asTeflon™.

(Points of Difference with Similar Technologies)

In Patent Document 4, a process to reform the property or sterilize onthe surface of an object by blowing out plasma to the object isdisclosed, the plasma generated by dielectric discharge from a plasmahead formed by bundling a plurality of dielectric thin tubes. Aplurality of plasma supply openings is equipped in the technologydisclosed in Patent Document 4, but gas inlets and electrodes togenerate plasma of each thin tube do not function independently. Andthere is no description to suggest a technology where gas inlets andelectrodes are independently equipped in each thin tube. Therefore it isnot easy to invent a technology according to the present inventionwherein a plurality of different plasmas is generated in a plurality ofplasma generation units, and plasma reaction is carried out in a spacebetween a plasma head and a substrate by referring to this document.

In Patent Document 5, a process to form an organic thin film includingmetal such as silicon oxide by a reaction of gas including metal such asTEOS and oxygen is disclosed. But the technology described in PatentDocument 5 is a technology wherein a thin film is formed by mixing andreacting reaction gas which is in plasma state and metal-including gaswhich is not in plasma state. Therefore this technology is differentfrom the technology of the present invention wherein a plasma head iscomposed of a plurality of unit parts installed in parallel, anddifferent plasmas are generated in each unit part, and film depositionis carried out by the reaction between the different plasmas. Thetechnology according to the present invention is a technology wherein aplurality of plasma supply openings to generate different plasmas can bevery closely and densely placed by stacking alternately a plurality ofdielectric members and electrodes. Therefore it is not easy to invent atechnology according to the present invention by referring to thisdocument.

INDUSTRIAL APPLICABILITY

As above mentioned, by using a CVD apparatus and a method for formingCVD film according to the present invention, low cost production of ahigh quality nitride film can be materialized for the purpose of, forexample, forming antireflection film of a solar battery, which makes ahuge contribution to the field of electronics.

PREFERRED EMBODIMENTS

Several embodiments of a method for forming CVD film according to thepresent invention are described in detail as follows, but the presentinvention is not limited to these embodiments.

Preferred Embodiment 1 (The First Test on Electrodes)

Minimum supply voltage necessary to spontaneously generate plasma wasmeasured by setting different several conditions for the ambient of ahollow portion and gas which flows in the flow passage plate in order toinvestigate optimum conditions for plasma generation for an electrode(upper electrode) with a hollow portion according to the presentinvention. For comparison, the voltage was measured for an electrodewithout a hollow portion. And also, a flow passage plate was formedusing ceramic members, and a gas flow passage was formed on the lateralside of the flow passage plate.

TABLE 1 Minimum RF power (W) necessary for spontaneously generatingplasma Gas (carrier gas) which flows in a flow passage plate Ambient ina Ar 85% Ar 70% hollow portion Ar 100% N₂ 15% N₂ 30% Ar gas enclosed at50 Torr 500(W) 900 2000 Ar gas enclosed at 250 Torr 700 1100 1800 Ar gasenclosed at 500 Torr 800 1600 2000 Ne gas enclosed at 50 Torr 400 10002200 Ne gas enclosed at 250 Torr 600 1100 1700 Ne gas enclosed at 500Torr 900 1500 2100 Atmospheric pressure 600 1500 1300 Vacuum 500 15002100 Without a hollow portion 600 1000 2100

In addition, members as follows were used for the components of adischarge electrode.

An electrode wire: a linear electrode wire made of Ni, one terminal wasconnected to a metal foil made of Mo, emitter material was not usedCeramic member: quartz

It was found that an optimum CVD condition was when RF power necessaryfor spontaneously generating plasma was less than or equal to 700 Wbecause spark discharge was not generated and plasma state was stable.And it was found that Ar gas not including N₂ was preferable for carriergas flowing in a flow passage plate to maintain stable plasma. And itwas found that vacuum or Ar gas enclosed at less than or equal to 250Torr was preferable as an ambient of a hollow portion. And according tothe other experiment using other gases as enclosed gas, excellent resultwas obtained when noble gas such as Ne was used as carrier gas andenclosed gas in the hollow portion, the result being similar to theresult when Ar was used.

Preferred Embodiment 2 (The Second Test on Electrodes)

Next, minimum RF power necessary for spontaneous plasma generation wasmeasured using an electrode formed according to the present invention bychanging the material of members and the condition of gas which flows ina flow passage plate. Discharge electrodes were equipped with hollowportions filled with noble gas at a pressure of 250 Torr. The flowpassage plate was made of heat resisting metal and flow passages wereformed along the side of the plate.

TABLE 2 Minimum RF power (W) necessary for spontaneously generatingplasma Gas (carrier gas) which flows in a flow passage plate Ambient ina Ar 85% Ar 70% hollow portion Ar 100% N₂ 15% N₂ 30% Condition 1 700(W)1000 1700 Condition 2 800 1100 1800 Condition 3 600 900 1600 Condition 4800 1000 1800 Condition 5 1000 1300 2100 Condition 6 700 1000 1700Condition 7 700 1100 1600 Condition 8 600 1000 1600 Condition 1: alinear electrode wire made of Ni alloy, one terminal was connected to ametal foil made of Mo, emitter material was not used, ceramic member wasmade of quartz, Ni—W alloy was used as Ni alloy. Condition 2: a linearelectrode wire made of Ni, one terminal was connected to a metal foilmade of Mo alloy, emitter material was not used, ceramic member was madeof quartz, Mo—W alloy was used as Mo alloy. Condition 3: a linearelectrode wire made of W including 1 weight % of Th, one terminal wasconnected to a metal foil made of Mo, emitter material was not used,ceramic member was made of quartz. Condition 4: a linear electrode wiremade of W including 4 weight % of Th, one terminal was connected to ametal foil made of Mo, emitter material was not used, ceramic member wasmade of quartz. Condition 5: a linear electrode wire made of W including10 weight % of Th, one terminal was connected to a metal foil made ofMo, emitter material was not used, ceramic member was made of quartz.Condition 6: a linear electrode wire made of W including 4 weight % ofThO, one terminal was connected to a metal foil made of Mo, emittermaterial was not used, ceramic member was made of quartz. Condition 7: alinear electrode wire made of Ni, one terminal was connected to a metalfoil made of Mo, emitter material was not used, ceramic member was madeof translucent alumina. Condition 8: a coiled electrode wire made of Ni,one terminal was connected to a metal foil made of Mo, emitter materialwas not used, ceramic member was made of quartz.

Preferred Embodiment 3 (The Third Test on Electrodes)

Next, minimum RF power necessary for spontaneous plasma generation wasmeasured using an electrode formed according to the present invention bychanging a layer made of emitter material formed on the surface of anelectrode wire and the condition of gas which flows in a flow passageplate. Discharge electrodes were equipped with hollow portions filledwith noble gas at a pressure of 250 Torr.

TABLE 3 Minimum RF power (W) necessary for spontaneously generatingplasma Gas (carrier gas) which flows in a flow passage plate Atmospherein a Ar 85% Ar 70% hollow portion Ar 100% N₂ 15% N₂ 30% Condition 9800(W) 1100 1800 Condition 10 600 900 1500 Condition 11 700 1000 1400Condition 12 700 900 1600 Condition 13 600 900 1600 Condition 14 7001000 1500 Condition 15 700 900 1400 Condition 9: a linear electrode wiremade of Ni, one terminal was connected to a metal foil made of Mo,emitter material was not used, ceramic member was made of quartz, Ni—Walloy was used as Ni alloy. Condition 10: a linear electrode wire madeof Ni, one terminal was connected to a metal foil made of Mo, emittermaterial was made of TiSrO having perovskite type crystal structureformed by glue coating and firing, ceramic member was made of quartz.Condition 11: a linear electrode wire made of Ni, one terminal wasconnected to a metal foil made of Mo, emitter material was made of MgOhaving perovskite type crystal structure formed by glue coating andfiring, ceramic member was made of quartz. Condition 12: a linearelectrode wire made of Ni, one terminal was connected to a metal foilmade of Mo, emitter material was made of TiO having perovskite typecrystal structure formed by glue coating and firing, ceramic member wasmade of quartz. Condition 13: a linear electrode wire made of Ni, oneterminal was connected to a metal foil made of Mo, emitter material wasmade of TiSrO having perovskite type crystal structure formed by MOCVD,ceramic member was made of quartz. Condition 14: a linear electrode wiremade of Ni, one terminal was connected to a metal foil made of Mo,emitter material was made of MgO having perovskite type crystalstructure formed by MOCVD, ceramic member was made of quartz. Condition15: a linear electrode wire made of Ni, one terminal was connected to ametal foil made of Mo, emitter material was made of TiO havingperovskite type crystal structure formed by MOCVD, ceramic member wasmade of quartz.

Preferred Embodiment 4 (The First Evaluation of Nitride Film)

When atmospheric pressure plasma is generated by supplying power from RFor LF power source via electrodes prepared for dielectric-barrierdischarge, it is possible to soften the collision energy of electrons orcharged reactive molecules which collide the surface of a substrate soas to control substrate damage and enhance desired reaction by, forexample, applying bias voltage to the lower electrode in addition tosimply applying appropriate effective voltage between the upperelectrode and the lower electrode. The film quality of silicon nitridefilm was evaluated which was deposited by applying bias voltage so thatplasma was generated not only between an electrode and a substrate butalso between an electrode and other electrode.

FIG. 9(a), FIG. 9(b), and FIG. 9(c) are cross-sectional diagrams of aplasma head in a CVD apparatus according to of the embodiment of thepresent invention. FIG. 9(a) is a diagram which shows a plasmageneration state when a substrate was connected to ground potential andpositive bias voltages and negative bias voltages were alternativelyapplied to a plurality of electrodes. FIG. 9(b) is a diagram which showsa plasma generation state when a substrate was connected to floatingpotential in FIG. 9(a). FIG. 9(c) is a diagram which shows a plasmageneration state when a substrate was connected to ground potential andpositive bias voltages were applied to all electrodes.

Film quality was evaluated. In the case of FIG. 9(a), stable plasma wasgenerated by glow discharge and a dense film was obtained. By contrast,in the case of FIG. 9(b) and FIG. 9(c), stable plasma was generated byglow discharge but a less dense film was obtained in comparison to FIG.9(a). In the case of FIG. 9(a), plasma is generated between neighboringelectrodes, plasma region is wide, and deposition rate is large. Anddeposited film presumably receives less damage because collision ofpositive ions to a substrate is weakened.

TABLE 4 The deposition rate of silicon nitride film and its film qualityevaluation (relative value) Conven- Film depsited according tional tothe present invention thermal FIG. FIG. FIG. CVD film 9(a) 9(b) 9(c)Upper electrode (+) voltage 200 (V) 200 200 Upper electrode (−) voltage0 0 NA Lower electrode (−) voltage 0 float  0 Deposition rate 10 20~4015~35 10~30 Etching rate 10 10~30 40~60 40~60Discharge electrode was made of the following members. Plasma excitationfrequency was 13.56 MHz.Electrode wires were placed in the hollow portion. The ambient of thehollow portion is vacuum state.Electrode wire: a linear electrode wire made of Ni, one terminal wasconnected to a metal foil made of Mo, emitter material was not used,ceramic member was made of quartz.

The technology according to the present invention was compared withnitride film deposition by conventional thermal CVD. In all the case ofbias voltage application as shown in FIG. 9(a), FIG. 9(b), and FIG.9(c), the increase of deposition rate was observed in the depositionmethod according to the present invention in comparison to theconventional method. Among these cases, especially high deposition ratewas observed in the method as shown in FIG. 9(a). In addition, etchingrate using buffered hydrofluoric acid for evaluation of the film qualityof deposited film. When etching rate is lower, film quality is shown asbeing denser. By thermal CVD, the deposition of denser film is possiblethough deposition rate is low. Among CVD methods according to thepresent invention using a plasma head as shown in FIG. 9(a), FIG. 9(b),and FIG. 9(c), especially the film quality was found to be the densestby the method as shown in FIG. 9(a).

Preferred Embodiment 5 (The Second Evaluation of Nitride Film)

The experiment of deposition and evaluation similar to the embodiment 4was done by changing plasma excitation frequency.

TABLE 5 Plasma excitation frequency: 10 MHz The deposition rate ofsilicon nitride film and its film quality evaluation (relative value)Film deposited according to the present invention FIG. 9(a) FIG. 9(b)FIG. 9(c) Upper electrode (+) voltage 200 (V) 200 200 Upper electrode(−) voltage 0 0 NA Lower electrode (−) voltage 0 float  0 Depositionrate 15~45 20~30 10~25 Etching rate 15~35 45~55 35~65

Preferred Embodiment 6

In order to relax the damage of a substrate due to the collision ofpositive ions such as Ar ions, the effect of a method was evaluated, themethod wherein a positive bias voltage was applied to the substrate.FIG. 10 is a cross-sectional diagram of a plasma head in a CVD apparatusaccording to the embodiment of the present invention. A dielectricsubstrate 325 was placed under the substrate 324, and an electrode forapplying bias voltage 326 was placed under the dielectric substrate.Positive bias voltage was applied by a power source 327 to the electrode326. And deposited film presumably receives less damage becausecollision of Ar positive ions 328 which moves from an electrode 322 to asubstrate 324 is presumably weakened. The experiment showed that thequality of the deposited film was denser when positive bias voltage wasapplied by a power source 327 in comparison to the case when it was notapplied.

TABLE 6 Plasma excitation frequency: 20 MHz The deposition rate ofsilicon nitride film and its film quality evaluation (relative value)Film deposited according to the present invention FIG. 9(a) FIG. 9(b)FIG. 9(c) Upper electrode (+) voltage 200 (V) 200 200 Upper electrode(−) voltage 0 0 NA Lower electrode (−) voltage 0 float  0 Depositionrate 20~45 15~30 15~35 Etching rate 20~35 40~50 45~65

Preferred Embodiment 7

In order to investigate a cooling effect by a discharge electrode, anelectrode temperature was measured after Ar gas plasma was generated forone hour under RF power of 2000W applied at 13.56 MHz. The electrodetemperature was 150° C. when cooling down was not done. On the otherhand, when cooling down was done using Ar gas or nitrogen gas, thetemperature was 50° C. and 60° C. respectively, which showed thatadequate cooling effect was obtained.

1. A discharge electrode composed of a ceramic member having a hollowportion where an electrode wire is placed without contact with theceramic member.
 2. The discharge electrode according to claim 1, whereinthe hollow portion is in vacuum state.
 3. The discharge electrodeaccording to claim 1, wherein gas is enclosed in the hollow portion andthe gas is noble gas.
 4. The discharge electrode according to claim 3,wherein the pressure in the hollow portion is reduced to less than orequal to 250 Torr.
 5. The discharge electrode according to claim 3,wherein the noble gas is Ar or Ne.
 6. The discharge electrode accordingto claim 1, wherein one terminal of the electrode wire was connected toa metal foil, the end of the metal foil functions as an externalextraction terminal, and the metal foil is sealed in contact withnarrowed part of the ceramic member.
 7. The discharge electrodeaccording to claim 1, wherein the electrode wire is made of Ni or Nialloy.
 8. The discharge electrode according to claim 1, wherein theelectrode wire is made of W including Th or ThO.
 9. The dischargeelectrode according to claim 8, wherein the content of Th is less thanor equal to 4 weight %.
 10. The discharge electrode according to claim1, wherein the electrode wire is formed with coil-like shape.
 11. Thedischarge electrode according to claim 1, wherein a layer made ofemitter material is formed on the surface of the electrode wire, and theemitter material is material with smaller work function than thematerial of the electrode.
 12. The discharge electrode according toclaim 11, wherein the emitter material is material with perovskite-typecrystal structure.
 13. The discharge electrode according to claim 11,wherein the emitter material is more than or equal to one chemicalcompound selected from the chemical compound group comprising TiSrO,MgO, TiO.
 14. The discharge electrode according to claim 11, wherein theemitter layer is formed by a process wherein material of emitter layeris torn into pieces in a mortar, and resultant powder is solved inwater, and the solution mixed with glue is coated on the surface of theelectrode wire, and emitter layer is formed by sintering of coated wire.15. The discharge electrode according to claim 11, wherein the emitterlayer is formed by MOCVD.
 16. The discharge electrode according to claim6, wherein the metal foil is made of Mo or Mo alloy.
 17. The dischargeelectrode according to claim 4, wherein the noble gas is Ar or Ne. 18.The discharge electrode according to claim 5, wherein one terminal ofthe electrode wire was connected to a metal foil, the end of the metalfoil functions as an external extraction terminal, and the metal foil issealed in contact with narrowed part of the ceramic member.
 19. Thedischarge electrode according to claim 6, wherein the electrode wire ismade of Ni or Ni alloy.
 20. The discharge electrode according to claim7, wherein the electrode wire is made of W including Th or ThO.